In many cases of restless legs syndrome (RLS) the exact cause is unknown.

When no cause can be found it is known as idiopathic, or primary restless legs syndrome. This can run in families and is most common in people younger than 40.

Dopamine

There is conflicting evidence about the role of a brain chemical called dopamine with restless legs syndrome.

Some people benefit from a type of medication called a dopamine agonist, which raises the levels of dopamine in the brain. This had led to some people arguing that the condition is related to problems with creating and breaking down dopamine in brain cells.

Dopamine levels naturally fall towards the end of the day, which may explain why the symptoms of restless legs syndrome are often worse in the evening and during the night.

Further research into this is needed. 

Underlying health condition

Secondary restless legs syndrome can occur as a complication of another health condition, or it can develop as a result of another health-related factor.

For example, you may develop secondary restless legs syndrome if you:

• have iron-deficiency anaemia – low levels of iron in the blood can lead to a drop in dopamine, triggering restless legs syndrome
• have a chronic (long-term) health condition – such as chronic kidney disease, diabetes, Parkinson’s disease, rheumatoid arthritis, an underactive thyroid gland or fibromyalgia  
• are pregnant – particularly from week 27 until birth; in most cases, the symptoms disappear within four weeks of giving birth

Triggers

There are a number of triggers that do not cause restless legs syndrome, but can make symptoms worse. These include medications such as:

• some antidepressants
• antipsychotic medicine
• lithium (used in the treatment of bipolar disorder)
• calcium channel blockers (used in the treatment of high blood pressure)
• some antihistamines
• metoclopramide (used to relieve nausea)

Other reported triggers include:

• excessive smoking, caffeine or alcohol
• being overweight or obese
• stress
• lack of exercise