Taking painkillers before a COVID-19 vaccine to prevent potential side effects is not recommended, the World Health Organization (WHO) has warned.
The WHO has reiterated its advice after misleading rumours continued to circulate online in Europe.
Several posts on social media have falsely promoted purported medicines that can alleviate the potential side effects of the coronavirus vaccine.
These included antihistamines and painkillers, which can usually be bought from pharmacies and shops.
"It is helpful to take an antihistamine before undergoing the vaccine," claimed one Italian user on Twitter.
But in a statement to Euronews, the WHO repeated that citizens are not advised to take painkillers before a jab as it might impact the efficacy of the vaccine.
"Taking painkillers such as paracetamol before receiving the COVID-19 vaccine to prevent side effects is not recommended," said a spokesperson.
"This is because it is not known how painkillers may affect how well the vaccine works."
"However, you may take paracetamol or other painkillers if you do develop side effects such as pain, fever, headache, or muscle aches after vaccination."
The common side effects of the vaccine, such as arm soreness, headaches, or tiredness, are minor in most cases, the WHO added.
But while antihistamines can mitigate certain allergic reactions, they are not designed to prevent them.
"There is no reason to take antihistamines to try and limit the symptoms you might get post-vaccination," said Professor Luke O’Neill, Chair of Biochemistry at Trinity College Dublin.
"In general, there is no reason to take medicine unless you are developing some kind of symptoms anyway."
"If you're already on any medication at all, you should check with your local doctor, as some people may be advised to keep taking antihistamines for rashes and other allergic reactions," Professor O'Neill told Euronews.
"But there's no reason to start taking painkillers ahead of the vaccine, just in case they might limit vaccine efficacy."