The HPCSA in December last year found Basson guilty of unprofessional conduct, with the hearing running till Saturday.
The HPCSA inquiry was held to determine whether he acted unethically in the exercise of his duties as a chemical warfare expert.
He was accused of acting unethically by being involved in the large-scale production of Mandrax, cocaine and teargas, of weaponising teargas, and of supplying it to Angola’s Unita leader Jonas Savimbi.
He was also accused of acting unethically by providing disorientating substances for cross-border kidnappings, and by making cyanide capsules available for distribution to operatives for use in committing suicide.
In 2002, Basson was acquitted by the High Court in Pretoria of criminal charges arising from his conduct.
The HPCSA reviewed the judgment to establish if there were grounds to continue with an inquiry.
The State appealed against this decision in the Supreme Court of Appeal, but the appeal was dismissed.
The State then went to the Constitutional Court, but the case was dismissed in September 2005.
Legal advocacy group Section27 said on Tuesday it would be giving evidence at the hearing on behalf of health professionals and civil society organisations.