An inquiry into the use of a controversial anti-malarial drug given to British military personnel is to begin taking evidence.
Mefloquine, or Lariam, is given to soldiers serving overseas but can cause anxiety, depression and nightmares.
The Defence Select Committee is investigating after concerns from some military personnel over its safety.
The government says it only prescribes Lariam after an individual risk assessment.
Its manufacturers Roche say the benefits of Lariam outweigh its risks.
The once-a-week anti-malarial tablet is issued to about 2,500 British service personnel a year, in accordance with Public Health England's guidance - although PHE recently said its guidance was not designed for "any specific occupational groups, including the military".
It is one of a number of different anti-malarial drugs used by the Ministry of Defence, and makes up 1.2% of the military's anti-malarial stocks.
Mefloquine is a once-a-week anti-malarial tablet, marketed by manufacturer Roche under the name Lariam.
It is licensed for sale in 42 countries worldwide, and is available under prescription in the UK.
It is one of a number of different tablets that protect against malaria - others include doxycycline (Vibramycin-D) and atovaquone plus proguanil. Lariam is often recommended to people travelling to areas where the malaria pathogen has become resistant to other anti-malarial agents.
Among the possible side-effects listed for Lariam are depression, paranoia, hallucinations, and psychosis - although it by no means affects everyone. It should not be prescribed to people with a history of depression or psychiatric disorders.
Roche advises patients and healthcare professionals to follow the advice it provides - and says a recent EU safety assessment found that the benefits of Lariam outweigh the potential risks.
The MoD says Lariam is not a "first-line drug", and is used primarily in cases where other drugs "would not be effective or appropriate for the person".
However, Dr Julian Lewis MP, chair of the Defence Select Committee, said the number of cases of military personnel reporting serious side-effects after taking Lariam was "deeply disturbing".
"It is clear that the drug does not command the universal support of members of our armed forces," he said.
The committee will be looking at what safety assessments the MoD made about Lariam, and how it dealt with military personnel who have suffered from detrimental side-effects.
A fellow committee member, Conservative MP Johnny Mercer, said he had heard from soldiers who threw away their tablets and risked contracting malaria, rather than take the drug.
In August, the former army officer called for the government to immediately stop issuing the drug until it was further investigated.
He said: "I've had a letter about once or twice a week from not only constituents but people all over the UK who have suffered or know someone who has suffered, they believe, as a result of taking Lariam."
This week the British Medical Journal published an article on Mefloquine saying that "it is almost certain neuropsychiatric events are more common with the drug than with other anti-malarials", adding that it "may be less suitable for combat troops".
'It's the worst form of friendly fire'
Major General Alastair Duncan, 63, of the Yorkshire Regiment, was given Lariam in 1999 before being deployed to Sierra Leone.
Prior to that he had been hurt in an explosion in Bosnia where he commanded British forces. He was later diagnosed with post-traumatic stress disorder (PTSD).
His wife Ellen believes that the drug "exacerbated" his condition, and contributed to him eventually being sectioned under the Mental Health Act.
"It's made him worse. He had PTSD and then Lariam made him more depressed and low, and it shouldn't be given to anyone else. There is an institutional denial at the MoD about how bad the effects can actually be", she said.
"We're still giving it to people and we know this is a time bomb for some people.
"Many many people are not affected but there are a sizable minority that will be and it may permanently damage their brain, so why are we using this? In my opinion it's the worst form of friendly fire."
The Ministry of Defence said it only ever prescribed Lariam after a risk assessment, where information about the individual - including medical history - is taken into consideration by the prescribing clinician.
On Tuesday, the inquiry will hear from heads of drug company Roche, Dr Frances Nichol and Mike Kindell.
In a statement, the company told the BBC it "can't comment on how the military currently prescribes Lariam, but believe care is required when doing so".
It points out that Lariam is approved by the World Health Organisation for sale in 42 countries.
A recent regular safety assessment conducted by EU health authorities reinforced previous guidance that the benefits of Lariam outweigh the potential risk of the treatment, it added.
The MoD has a stockpile of more than 11,500 packs of the drug, according to a parliamentary question and answer.
In response to a written question from the Defence Select Committee, Michael Fallon has said the MoD's use of Lariam is under "continual review".
While it was not disputed that the drug had side-effects, there was "no evidence that mefloquine causes PTSD", the defence secretary said.
He added that all anti-malarial drugs have side-effects, and there had to be a balance between providing protection against malaria and side-effects.
An MoD spokesperson said: "Mefloquine is not the first drug of choice for our personnel and is only ever prescribed after an individual risk assessment.
"It is used by civilians and military personnel throughout the world and there are no countries where the drug has had its licence withdrawn on safety grounds."