So far there has been no causal link between coronavirus vaccines and menstrual disorders, Europe's drugs regulator said on Friday, separately recommending that three new conditions be added as possible side-effects of J&J's coronavirus shot.

The European Medicines Agency (EMA) said its safety committee had studied cases of menstrual disorders reported after vaccination, adding it had requested more data from vaccine developers to assess the issue.

Menstrual disorders can occur for various reasons, from stress and tiredness to underlying medical conditions such as fibroids and endometriosis.

Separately, the EMA on Friday recommended that immune thrombocytopenia, or low blood platelets, dizziness and tinnitus, or ringing in the ear, be added to the labels of J&J's single-shot vaccine as potential adverse reactions.

The EMA stressed that the benefits of J&J's vaccine still outweighed any risks, adding that it had analyzed 1,183 cases of dizziness and more than 100 cases of tinnitus to reach its conclusion.

The company did not immediately respond to Reuters' request for comment.

The EMA last month listed a rare nerve-degenerating disorder, Guillain-Barré syndrome (GBS), as a possible rare side-effect from the J&J shot. The U.S.-based company has also struggled with supply in the European Union.

The EMA has also added GBS as a possible side-effect of AstraZeneca's COVID-19 vaccine and said on Friday it was still monitoring such reports.

Both the J&J and AstraZeneca vaccines use similar technology but with different versions of a cold virus to deliver immunity-building instructions to the body.