Boosting your intake of antioxidants (chemicals that block the action of free radicals) can also help — these are found in fresh fruit and vegetables, and green tea.

Topically applied anti-androgen hormones can be effective as they block the action of androgen, the principle hormone responsible for hair loss.

Fly spray contains chemicals (including many organophosphate compounds) that bind to and permanently block the action of an enzyme called acetylcholinesterase.

Both lamivudine and zidovudine are reverse transcriptase inhibitors, which block the action of an enzyme, reverse transcriptase, that the virus requires for reproduction.

Leukotriene antagonists (such as montelukast and zafirlukast) block the action of leukotriene mediators and are being used increasingly in allergic diseases.