Hold your horses, Botox. You’re not ready for migraines just yet.

According to reports, UK health regulators are asking Allergan, the maker of the anti-wrinkle drug, for more evidence to confirm its effectiveness against chronic migraine headaches.

Based on reports, the current clinical findings are small and the results are “biased.” The National Institute for Health and Clinical Excellence said that the participants may have been aware that they were getting Botox instead of the using the placebo effect.

Pending further studies, the National Health Service will not be able to approve Botox for migraine application.