Under international law that is? The Guardian seems to think so:
Nearly half of death row prisoners were sentenced for drugs trafficking – a punishment that violates international law
That might be wishful thinking on their part.
While ‘limitation to the most serious crimes’ is an established principle of international law, the term lacks overall definition and agreement. The UN General Assembly has endorsed a set of Safeguards guaranteeing the protection of the rights of those facing the death penalty which stipulates that ‘the most serious crimes’ only applies to international crimes with lethal or other extremely grave consequences. The UN Special Rapporteur on Extrajudicial, Summary or Arbitrary Executions has similarly stated that the death penalty should be eliminated for economic crimes, drug-related offences, victimless offences and actions relating to moral values including adultery, prostitution and sexual orientation. This interpretation is contested by a number of countries.
A pronunciamento from a UN bureaucrat does not international law make.