Two people have died after taking synthetic cannabis in Queensland in the past two days.

A 33-year-old Mackay man passed away after taking it yesterday and late this afternoon a 41-year-old man, unknown to the first also died.

Adding to the intrigue, he was a witness set to give evidence in a murder trial.

9NEWS understands both men bought the product known as "Full Moon" masked as herbal tea from a Mackay sex shop, but similar products can be bought at convenience stores and on international websites.

Synthetic cannabis is often marketed as innocent things like herbal incense and potpourri but it is illegal.

Laws introduced in Queensland in 2013 ban all synthetic drugs that have the same intended effect as a dangerous drug.

The Mackay Base Hospital has seen an increase people suffering effects of synthetic drugs.