Are Muscle Relaxants or Magnesium Necessary for Physiotherapy — and Why Do Painkillers Make Assessment Harder?

Should you take a muscle relaxant or magnesium supplement before physiotherapy? And why can taking painkillers beforehand make it harder for your physiotherapist to find the real cause?

Many people regularly take muscle relaxants or magnesium supplements to ease aches before seeing a physiotherapist. But are these actually necessary — and why does taking a painkiller beforehand sometimes make the assessment harder, not easier?

Muscle relaxants and magnesium supplements are not necessary for physiotherapy — the evidence supporting their benefit is quite weak. Painkillers, while they make you more comfortable, can make it harder for a physiotherapist to locate the actual source of your pain if taken before a first assessment.

A meta-analysis published in the BMJ, pooling 49 trials, found very low-certainty evidence for the effectiveness of muscle relaxants for back pain — the difference from placebo was too small to be clinically meaningful.[1]

At the same time, muscle relaxants carry a real risk of central nervous system side effects — drowsiness, dizziness — and some types carry a risk of dependence with longer-term use.[1]

In short, muscle relaxants are not something you need to take before physiotherapy. If a doctor has prescribed one for short-term symptom relief, that's fine to follow — but it shouldn't be used as a substitute for addressing the underlying cause.

A Cochrane meta-analysis reviewing 11 trials found that magnesium supplementation did not meaningfully reduce muscle cramps compared to placebo.[2]

There's some preliminary evidence it may modestly help with delayed-onset muscle soreness (DOMS) after intense exercise, but the research base is still too limited for a general recommendation.

In short, you don't need magnesium supplements before physiotherapy — unless a doctor has confirmed an actual magnesium deficiency, which is uncommon in the general population.

• Physiotherapy assessment relies on pain as a signal — physiotherapists use "pain provocation" tests: pressing on specific spots, or moving you into certain positions, to see exactly what reproduces or worsens your symptoms and pinpoint the real source.

• Painkillers mask that signal — if you've taken pain medication beforehand, the pain that should appear during testing may not show up, or may be dulled, producing a "false negative" result.

• This can lead to a treatment plan that misses the target — if the physiotherapist can't clearly identify what position or structure triggers your pain, they may end up treating the wrong area, or misjudge how severe the issue actually is.

• It can also mask important warning signs — some painkillers may dull symptoms that would otherwise flag a more serious underlying condition, delaying an appropriate referral.