What is it?

Capsaicin is taken from chilli peppers. It works mainly by reducing Substance P, a pain transmitter in your nerves. Results from RCTs assessing its role in treating osteoarthritis suggest that it can be effective in reducing pain and tenderness in affected joints, and it has no major safety problems. Evidence for its effectiveness for fibromyalgia is related to a single trial.

  • Family: Herbal medicine extracted from chilli peppers (Capsicum family)
  • Scientific name: Capsaicin
  • Other names: Axsain®, Zacin®, chilli, pepper gel, cayenne

Capsaicin is the main medicinally active component of chilli peppers which is taken from the plant’s tissues. It’s licensed in the UK for osteoarthritis and you can get it on prescription in the form of gels, creams and plasters.

How does it work?

Several studies have found that capsaicin can use up Substance P. Substance P plays an important role in transmitting pain signals from nerve endings to your brain. It’s also involved in activating inflammatory substances in joints.

Is it safe?

There are no major safety concerns in applying capsaicin gel/cream. You may feel a burning sensation when the gel touches your skin. This is because capsaicin also binds to specific receptors in nerve endings called VR1, producing a burning sensation which isn’t caused by any tissue damage. Brief skin redness is common, but high doses of capsaicin can cause skin blisters.

A review of capsaicin applied to the skin to treat chronic pain (not specifically related to osteoarthritis, rheumatoid arthritis or fibromyalgia) concluded that around one third of people experience a reaction around the area where the treatment is applied.

It’s important to keep capsaicin away from your eyes, mouth and open wounds because it will cause irritation. There have been no reported drug interactions.

Most trials have used either 0.025% or 0.075% of capsaicin gel applied to the skin four times a day.

Capsaicin trials for osteoarthritis

Review article (1994)

The trials included in this article investigated the effectiveness of capsaicin gel in treating osteoarthritis when compared to a placebo gel. Capsaicin was applied four times a day (0.025% in two trials and 0.075% in one). The treatment period ranged from 4 to 12 weeks.

  • Capsaicin was found to be more effective than the placebo in all three trials.
  • Data from the trials was analysed together to get a single estimate of effectiveness. It was found that capsaicin was four times more effective in improving pain and joint tenderness in participants with osteoarthritis as compared to placebo gel.

Trial 1 (1994)

A trial not included in the above review randomly selected 113 people with osteoarthritis to apply either capsaicin cream or a placebo to their affected joint four times a day for 12 weeks.

  • Significantly more participants using capsaicin cream had a reduction in pain, as assessed by a doctor and by the participants themselves.
  • The severity of pain and joint tenderness was significantly reduced in participants using capsaicin.

Trial 2 (2000)

In an RCT published in 2000, 200 participants with osteoarthritis were randomly selected to apply one of the following to their affected joint for six weeks:

  • 0.025% capsaicin cream
  • glyceryl trinitrate cream
  • a cream containing both ingredients
  • a placebo cream.

The trial found the following:

  • Participants given any of the three active treatments had a significant reduction of both joint pain and painkiller use compared to participants who received the placebo cream.
  • Participants who used the cream that contained both active treatments had the greatest improvement in pain and the most significant reduction of painkiller use.

Similar beneficial results were found in another RCT, which evaluated the effectiveness of an ointment containing several herbal compounds, including 0.015% capsaicin (Arthritis Relief Plus), in treating joint pain and stiffness in 36 people with osteoarthritis.

Trial 3‡

In the most recent trial, 100 women with mild to moderate osteoarthritis of the knee received either 0.0125% capsaicin gel or a placebo gel three times a day for four weeks. This was followed by one week with no treatment, then another four weeks of the treatment they hadn’t previously used.

Compared to the placebo gel, greater improvements in the following were reported in relation to the capsaicin gel:

  • pain
  • stiffness
  • function.

‡ A trial of low quality. Results of this trial were given a lower weighting when we came to our conclusion about the compound.

Capsaicin trials for fibromyalgia

In this trial, 45 participants with fibromyalgia were randomised to apply either 0.025% capsaicin gel or placebo gel to areas with pain four times a day for four weeks.

Participants who used capsaicin reported less tenderness and experienced significant increase in grip strength when compared to participants on the placebo.