Ugandan government chemists are carrying out tests on a birthday cake, sweets and mangoes that opposition activists tried to offer the president to see if they contained poison, police said.
The youth activists attempted to throw a public birthday party for President Yoweri Museveni last month to focus attention on his disputed age.
But the 20-strong group was confronted by 200 heavily armed riot police and the gifts were seized.
“The cake and other gifts are with government chemists,” Kampala police spokesman Ibn Ssenkumbi said, Reuters reports.
“Examination will prove to us whether these edibles were in a good condition or whether there were actually some intoxicants inside them. That cake didn’t look in a condition to be eaten by a person.”
The group says Museveni is 73, not the 67 that is officially said, which would make him ineligible to run for office again.
Under Ugandan law, candidates must be under 75 and the next presidential election is due in 2016.
The activists say they can prove that Museveni, who has been in power since 1986, is 73 from school records and accounts from his friends.
Many older people in African countries do not know their exact dates of birth because of a lack of proper records.
The opposition group told local media they had not asked for official permission for the party because they wanted it to be a surprise for the president.
Ssenkumbi confirmed local media reports that it was possible the activists could be charged with “annoying the person of the president” but said any charges would only be decided on after the tests on the cake were finished.