The Russian dropped the bombshell at a press conference in Los Angeles on Monday and is now waiting to find out what sanction she will face.
Nike acted swiftly, suspending its contract with the five-time grand slam champion, while watchmaker Tag Heuer and luxury car brand Porsche followed suit.
A statement from sportswear giant Nike read: “We are saddened and surprised by the news about Maria Sharapova.
“We have decided to suspend our relationship with Maria while the investigation continues. We will continue to monitor the situation.”
Tag Heuer has severed ties altogether, with a statement reading: “Maria Sharapova was under contract with TAG Heuer until December 31, 2015. We had been in talks to extend our collaboration.
“In view of the current situation, the Swiss watch brand has suspended negotiations, and has decided not to renew the contract with Ms Sharapova.”
Porsche signed Sharapova as its first global endorser in 2013, and said in a statement: “We are saddened by the recent news announced by Maria Sharapova.
“Until further details are released and we can analyse the situation, we have chosen to postpone planned activities.”
The Russian has been the highest-earning female athlete in the world for the last 11 years, with her off-court endorsements dwarfing her income from prize money.
According to Forbes, the 28-year-old earned some €27m in 2015.
Among Sharapova’s other sponsors, the water brand Evian ostensibly stuck by her, saying in a statement: “We were surprised by the announcement of Maria Sharapova during her press conference.
“Evian has been a partner of Maria Sharapova for many years and until now we have maintained a trustworthy professional relationship.
“Evian attaches great importance to health, to integrity, and to transparence, and we will follow closely the development of the investigation.”
Cosmetics firm Avon, meanwhile, declined to comment.
With the assembled media expecting a retirement announcement on Monday, Sharapova revealed she had tested positive for meldonium following her quarter-final defeat against Serena Williams at the Australian Open in January.
Meldonium, which Sharapova said she had legally taken for 10 years, was placed on the banned list by the World Anti-Doping Agency (WADA) at the beginning of the year following “evidence of its use by athletes with the intention of enhancing performance”.
Sharapova claimed she had not read the updated list of banned substances sent to athletes in December and took “full responsibility” for her actions.
She is one of a number of Russian athletes to have fallen foul of the new rules on meldonium, and revelations about the drug since her announcement have raised more questions than answers.
Use of the drug was monitored by WADA last year following suspicions. A study has reportedly shown it was present in the system of 17% of Russians tested and 2.2% of all athletes.
Sharapova claimed she was prescribed meldonium, also known as mildronate, by her doctor in 2006 to deal with health issues such as an irregular heartbeat and a history of diabetes in her family.
One of the other major questions arising is why Sharapova was prescribed a medicine that is not licensed in the US, where she has been based since the age of seven.
The drug company that manufacturers it, meanwhile, has stated that it should normally only be taken for between four and six weeks at a time.
The International Tennis Federation said Sharapova had been informed of the positive test on March 2 and will be provisionally suspended from March 12.
Sharapova has waived the right to have her B sample tested and she and her team will instead hope everything she has done so far will limit the sanction she is given.
The next step is for an independent tribunal to be established to hear the case. A decision would be expected around two weeks after the hearing.