Sinclair was inspired by a family member’s experience with endometriosis to look into the use of cannabis as a pain management strategy. In 2017, he was part of a team, led by Dr Mike Armour (see Here's Why Menstruation Matters), that used an online survey to investigate self-management strategies Australians with endometriosis were using to relieve their pain. These strategies ranged from heat packs to meditation, but more than one tenth of the 484 respondents also used illicit cannabis. When the women rated the pain reduction for each method they had tried, cannabis was ranked the most effective, scoring 7.6 out of 10. Many cannabis users had more than halved their prescription medicines and reported other benefits including better sleep, reduced nausea, and less anxiety and depression.��

A similar survey of New Zealand endometriosis patients strengthened these findings, but this time, Sinclair and a larger international team examined which prescribed drugs cannabis users were using less. Opioids, a highly addictive analgesic medicine, were the most common type of painkiller that approximately 40% of women stopped taking. There was also a 15% reduction in the use of benzodiazepines, a potentially addictive sedative, a 17% reduction in non-steroidal anti-inflammatory drugs, and a 16% reduction in antidepressants. “This substitution effect is appearing more often in the literature,” explains Sinclair. “Women are replacing their normal medications with cannabis because they don’t like the side effects of the prescribed drugs or are worried about becoming addicted or dependent.” He adds a note of caution: “they may not be disclosing their therapeutic use of cannabis to their doctors, and as such, may not be aware that cannabis is not an appropriate medicine for everyone, or of the potential interactions cannabis has with other medicines, or that some medicines cannot be stopped abruptly. It really is crucial that this is done under the supervision and care of a medical doctor.”

Sinclair is now conducting an international survey on cannabis usage for endometriosis, in conjuntion with endometriosis support groups worldwide. “Specific questions around effectiveness, side effects, the types of cannabis products they use and how they take them will help us identify the most successful self-management trends. These will provide the basis for designing products for clinical trial,” Sinclair says.

There are more than 140 cannabinoids across the Cannabis genus, but research has mainly focused on cannabidiol (CBD) and the intoxicating delta-9-tetrahydrocannabinol (THC). Further research could uncover new therapeutics, more efficient cultivation techniques, and optimum dosing methods, which will make a critical difference to patients. “Cannabis products taken orally may not act for up to two hours,” says Sinclair, “but the effects can last between six to eight hours, meaning someone could get a full night’s pain-free sleep.” The rising interest in cannabis could also encourage innovative uses of other medicinal plants. “I believe researchers worldwide have looked into the medicinal properties of less than 10% of the 300,000-plus flowering plant species worldwide,” he adds. At the Institute's Herbal Analysis and Pharmacology Lab, Sinclair has joined a team investigating how the anti-inflammatory effects of CBD change when combined with terpenes, the compounds behind the strong smell of herbs such as rosemary and lavender. Such lab work provides the molecular insights needed to design products for clinical trials.

In January 2020 in Melbourne, Sinclair presented evidence at the Senate inquiry into the current barriers to patient access to medicinal cannabis in Australia, highlighting the lack of unbiased education and the dearth of doctors willing to prescribe it, particularly in rural communities. The inquiry resulted in 20 recommendations to break down these barriers, including a safety review of cannabidiol that downgraded it from a prescription-only drug to one that, in certain forms and for certain conditions, can be bought from a pharmacist. But some legal hurdles still need to be overcome. “Unless the drug driving test detects for actual impairment rather than the mere presence of THC, patients will be too afraid of losing their licence to use a potentially life-changing and now legal medicine,” says Sinclair.

Through his ongoing research and collaborations, Sinclair hopes to prove and promote the positive effects of medicinal cannabis. “Endometriosis is a horrible reality, and for many women the prescribed medicines do not work,” he says. “I would love to be part of the research team to provide such evidence, and allow doctors to have the evidence they need to give patients other options.”