Off-Label & Supportive Medications in PLS

Off-label prescribing is how medicine works at the edges of what has been formally studied. When no drug has been approved for a condition, and symptoms are real and impairing, clinicians sometimes reach for medications approved for other purposes that have a plausible biological rationale — or that have evidence in similar conditions. This page documents what is used off-label in PLS and related motor neuron disease, what the evidence actually says, and where you need to have a direct conversation with your neurologist before drawing any conclusions.

What "off-label" means and why it happens

Every drug approved by the FDA (or equivalent agencies) is approved for specific indications, doses, and patient populations — defined by the clinical trials that established its evidence base. When a physician prescribes a drug for a condition, dose, or population not included in that approval, that is off-label prescribing. It is not illegal, and it is very common: estimates suggest 20% of all prescriptions in the US are off-label.

Off-label prescribing happens in PLS for several reasons:

• PLS has no disease-modifying treatment and relatively few drugs approved for its symptomatic management. Clinicians are working with a limited toolkit.
• PLS overlaps biologically with ALS, MS, HSP, and other upper motor neuron conditions — and drugs studied in those conditions are sometimes extrapolated to PLS by clinicians managing patients without specific PLS evidence.
• The PLS patient population is too small to make it commercially attractive to run controlled trials for most symptomatic medications, so formal PLS-specific evidence is unlikely to appear even for widely used drugs.

The honest framing throughout this page: almost none of the medications described here have controlled evidence specifically in PLS. The evidence comes from ALS trials, general upper motor neuron condition studies, or clinical experience. Where that applies, we say so.

Off-label medications for muscle cramps

Muscle cramps — painful, involuntary contractions — occur in many PLS patients and can significantly impair sleep and quality of life. They are a more prominent feature of ALS (where lower motor neuron degeneration contributes to fasciculations and cramps), but are reported in PLS as well. The evidence base for cramp management is almost entirely from ALS studies.

Mexiletine — Evidence level: Emerging (for ALS cramps)

Mexiletine is an oral antiarrhythmic drug that works by blocking fast sodium channels, reducing abnormal electrical firing in excitable cells — including motor neurons. It has the most evidence of any drug specifically for cramps in ALS.

Multiple clinical trials in ALS have shown that mexiletine significantly reduces cramp frequency and severity. The evidence is strong enough that mexiletine is recommended in ALS management guidelines for cramp-predominant presentations. Standard doses range from 150 mg twice daily to 300 mg three times daily, titrated for effect and tolerability.

Side effects include nausea, dizziness, and tremor. Mexiletine has cardiac effects and is contraindicated in patients with significant cardiac arrhythmias or second or third degree AV block. An ECG is typically obtained before initiating treatment.

In PLS, mexiletine is used by some neurologists for patients with significant cramping, extrapolating from the ALS evidence. The mechanism (sodium channel blockade reducing motor neuron hyperexcitability) is plausible in PLS. There is no controlled PLS-specific trial for mexiletine. The ranolazine trial currently under study in ALS (see the emerging drugs page) uses a similar mechanistic approach.

Quinine sulfate — Evidence level: Anecdotal to Limited

Quinine was historically used for cramps in ALS and other conditions, with some trial evidence of modest benefit. However, the FDA has warned against quinine use for leg cramps due to serious adverse effects including thrombocytopenia (dangerously low platelet counts), cardiac arrhythmias, and hypoglycemia. Most current ALS guidelines do not recommend quinine for cramps given the risk profile, and safer alternatives like mexiletine are preferred. It is mentioned here because some patients encounter it in older literature.

Magnesium — Evidence level: Anecdotal

Magnesium supplementation is widely used by patients for cramps, based on general medicine experience (magnesium deficiency can cause cramps in healthy people) and anecdotal reports. There is no controlled evidence for magnesium in ALS or PLS cramps. Magnesium is generally safe at standard doses (taking excessive doses causes diarrhea) and is widely discussed in patient communities. The evidence is anecdotal; it cannot be recommended or dismissed on the basis of data.

Pickle juice — Evidence level: Anecdotal

Anecdotal reports of pickle juice (or other acetic acid preparations) terminating acute cramps rapidly have led to some interest in this as a home remedy. The proposed mechanism involves a reflex triggered by the acetic acid in the oropharynx rather than any systemic electrolyte effect. A small sports medicine study in healthy individuals supported the reflex hypothesis, but there is no evidence in MND specifically. It is harmless and widely used by patients; it is listed here to acknowledge what patients actually use rather than pretend the question doesn't come up.

Off-label for spasticity beyond standard therapy

Baclofen and tizanidine are the established first-line treatments for spasticity in PLS and are covered on the current treatments page. Several medications are occasionally used off-label when standard treatments are insufficient or not tolerated.

Dantrolene — Evidence level: Limited

Dantrolene works by a completely different mechanism from baclofen and tizanidine — it acts directly on muscle by inhibiting calcium release from the sarcoplasmic reticulum, reducing the muscle's ability to contract. It is approved for malignant hyperthermia and severe spasticity in conditions like cerebral palsy and MS.

In PLS and ALS, dantrolene is used rarely and cautiously because its primary side effect — significant muscle weakness — is particularly problematic in motor neuron disease, where weakness is already a concern. Hepatotoxicity (liver damage) is a serious risk with long-term use and requires monitoring. Dantrolene may be considered in exceptional cases of severe, refractory spasticity where the functional cost of the spasticity clearly outweighs the risk of additional weakness — but this is a narrow and carefully considered clinical decision.

Cannabidiol (CBD) and cannabis-based products — Evidence level: Anecdotal to Limited

Cannabis-derived medications and CBD are widely used by patients with spasticity across a range of neurological conditions. In multiple sclerosis, nabiximols (Sativex) — an oral spray combining THC and CBD — has regulatory approval for spasticity in several countries (though not in the US) based on controlled trial evidence.

In ALS and PLS specifically, the evidence base is limited. Some patients report benefit for spasticity, cramps, and pain. There is limited controlled trial evidence in ALS or PLS. The route of administration matters: inhaled cannabis smoke is generally contraindicated in patients with any respiratory vulnerability, and patients with MND should discuss respiratory status with their physician before considering any inhalation-based approach. Oral preparations (CBD oil, THC-containing edibles, nabiximols where available) are a different matter. Where legal and accessible, some neurologists take a pragmatic approach if conventional spasticity management is inadequate and respiratory function is preserved.

Gabapentin — Evidence level: Limited (for spasticity); Emerging (for neuropathic pain)

Gabapentin (and pregabalin, its successor) is widely used for neuropathic pain and is also used off-label for spasticity in some upper motor neuron conditions. In ALS, some clinicians use gabapentin for spasticity or pain management. The evidence for spasticity reduction is weak — gabapentin is not primarily an antispasticity drug. For neuropathic pain components or uncomfortable spasms, its rationale is stronger. In PLS, gabapentin is occasionally prescribed for the uncomfortable sensory components of spasticity (the feeling of tightness or discomfort) rather than to reduce tone per se.

Diazepam and clonazepam — Evidence level: Anecdotal

Benzodiazepines have antispasticity properties through their effects on GABA-A receptors. They are sometimes used as adjuncts for spasticity — particularly at night, when spasms may disrupt sleep. Clonazepam at a low dose at bedtime is used by some clinicians for this purpose. Diazepam is similarly used for acute or painful spasm episodes.

The significant concerns are sedation (a particular risk in patients who drive or manage cognitively demanding activities), dependence, and in patients with MND, the respiratory depressant effects of benzodiazepines in higher doses. These are not medications to be started or adjusted without careful discussion with a prescriber who understands your respiratory status. The evidence base for their use in PLS specifically is anecdotal.

Off-label for sialorrhea (drooling)

Sialorrhea in motor neuron disease is not caused by excess saliva production, but by impaired swallowing of normal volumes of saliva due to bulbar muscle weakness. It occurs in PLS patients with significant corticobulbar involvement and can cause social embarrassment, skin irritation around the mouth, and aspiration risk. Management is important and several approaches are used.

Anticholinergic medications — Evidence level: Limited to Emerging

Anticholinergic drugs reduce saliva production by blocking the muscarinic receptors that drive salivary gland secretion. Several are used off-label:

• Glycopyrrolate (Robinul) 1–2 mg every four hours is the most commonly used option. Its limited blood-brain barrier penetration means it causes less drowsiness than other anticholinergics — a practical advantage. Side effects include dry mouth (the intended effect, taken further), constipation, urinary retention, and blurred vision.
• Amitriptyline 10–25 mg (a tricyclic antidepressant with significant anticholinergic properties) is first-line at many MND centres for mild sialorrhea, particularly in patients who also have pseudobulbar affect or disturbed sleep — since it addresses multiple symptoms simultaneously. It can be started at 10 mg at bedtime and increased slowly.
• Scopolamine transdermal patch (1.5 mg/72 hours) reduces saliva by 75–80% but causes skin reactions requiring discontinuation in approximately 20% of patients. It is an option for patients who cannot tolerate oral medications.
• Atropine drops sublingual — ophthalmic atropine drops (1%) placed under the tongue is an off-label approach used by some MND centres, particularly in palliative settings. This is atropine used for an entirely different purpose than its ophthalmic approval; it should only be done under physician guidance.

All anticholinergics can thicken posterior secretions (mucus in the throat), which can worsen a different symptom — thick secretion management — while treating drooling. The balance between these effects needs clinical monitoring.

Botulinum toxin injections — Evidence level: Emerging

Botulinum toxin (Botox, Dysport, or Myobloc) injected directly into the parotid and submandibular salivary glands reduces saliva production through local paralysis of the secretory muscles. Randomized controlled trials in ALS have shown both type A and type B botulinum toxin are effective for sialorrhea, with similar efficacy between types. Injections typically need to be repeated every three months as the effect wears off.

The advantages of botulinum toxin for sialorrhea are: no systemic anticholinergic side effects, no drug-drug interactions, and direct, predictable local effect. The disadvantages are: it requires specialist injection (typically by a neurologist or maxillofacial surgeon with experience in salivary gland injection), and may not be available in all centres. This is arguably the most evidence-supported off-label option for sialorrhea in MND.

Off-label for fatigue

Fatigue is reported by a significant proportion of PLS patients and can be a major source of reduced quality of life independent of motor disability. It is inadequately studied and inadequately treated. There are very limited off-label options with any evidence base.

Modafinil — Evidence level: Anecdotal (for MND fatigue)

Modafinil is a wakefulness-promoting agent approved for narcolepsy and other sleep disorders. It has been studied in MS-associated fatigue with modest evidence of benefit. In ALS and PLS, some clinicians use it off-label for fatigue, but controlled evidence in MND does not exist. It is generally well tolerated. The main considerations are its stimulant properties (potential for sleep disruption if taken too late in the day), interactions with other medications, and its Schedule IV controlled substance status (requiring a specific prescription in most jurisdictions).

Bupropion — Evidence level: Anecdotal

Bupropion is an antidepressant that also has dopaminergic and noradrenergic activity that can reduce fatigue as a secondary effect. It is used off-label for fatigue in some MND patients, particularly when there is a concurrent mood component. The evidence in PLS or ALS specifically is essentially anecdotal — there are no controlled trials. Its clinical use in MND for fatigue is based on extrapolation from depression and MS literature.

Off-label for pseudobulbar affect — before and alongside Nuedexta

Pseudobulbar affect (PBA) — involuntary episodes of laughing or crying disproportionate to emotional state — has an FDA-approved treatment: Nuedexta (dextromethorphan/quinidine 20 mg/10 mg twice daily). Before Nuedexta's approval and as alternatives when it is not accessible or not tolerated, two off-label options have a long clinical history:

Amitriptyline — Evidence level: Limited (off-label for PBA)

Amitriptyline is a tricyclic antidepressant with a long history of use for PBA in motor neuron disease, predating Nuedexta's approval. It is the first-line option for PBA at some MND centres, particularly when the patient also has sialorrhea or disturbed sleep — since a single medication can address multiple symptoms. The evidence is from observational data and clinical experience rather than controlled trials for PBA in PLS specifically.

SSRIs and SNRIs — Evidence level: Limited

Selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine and paroxetine, and SNRIs such as venlafaxine, have been used off-label for PBA based on clinical experience and limited observational data. They are generally well tolerated. Nuedexta is typically preferred where available because it has the most controlled evidence specifically for PBA, but SSRIs remain a reasonable alternative when Nuedexta is not suitable (drug interactions, cost, access).

The important honest caveat

Almost all off-label use described on this page has no controlled evidence in PLS specifically. The best evidence — mexiletine for cramps, botulinum toxin for sialorrhea, amitriptyline for PBA — comes from ALS or general upper motor neuron disease contexts. The evidence is extrapolated to PLS on the basis of shared pathophysiology, not PLS-specific trials.

This does not mean off-label use is inappropriate — it means it requires informed clinical judgment applied to the individual patient's situation. It means any off-label treatment should be discussed explicitly with your neurologist: what the rationale is, what you are monitoring to assess benefit and harm, and what the plan is if the treatment is not helping.

It also means that if you are being offered an off-label treatment by a provider making strong claims about its effectiveness — particularly claims not grounded in any published evidence, or coupled with a significant financial transaction — appropriate skepticism is warranted. The drugs described on this page are used by knowledgeable neurologists at major MND centres because they have some clinical rationale; they are not secret cures being withheld by the mainstream.