Marijuana use in pregnancy may raise risks of addiction for baby boys

Smoking weed during pregnancy could put a developing baby at higher risk of addiction – but only if it’s a boy, rat study suggests

  • In recent years, the number of American women using marijuana in pregnancy has been on the rise, despite many doctors’ advice against doing so 
  • Little is known about how a pregnant woman’s marijuana use affects her fetus
  • An Italian study found that the brains of rats exposed to THC, weed’s psychoactive ingredient, in the womb produce more dopamine 
  • But the phenomenon was only true in male rats, the Cagliari University study found 
  • Excess dopamine is linked to greater risk for addiction and risk-taking behavior

Using cannabis during pregnancy could cause harmful brain changes to a developing baby – but only if it’s a boy, a new study in rats suggests.  

Male rats exposed to THC – the ingredient in marijuana that gets users high – while in the womb produced more dopamine as they grew up.

In humans the neuro-transmitter increases pleasure from activities such as gambling, sex and addiction.

The experiments found it altered the brains and behavior of the lab rodents. The same did not apply to female offspring, say the international team.

Corresponding author Dr Miriam Melis, of Cagliari University in Monserrato, said exposure to the drug in the womb may fuel risk-taking behaviors in teenage boys.

When developing rats were exposed to THC, weed’s active ingredient, in the womb, their brains made excess dopamine, which could raise their risks for addiction – but it only held true for males, Cagliari University scientists found 

Cannabis is the most widely used drug by women at reproductive age – and not just for recreational purposes. Up to one-in-seven take it during pregnancy.

As legal access grows it has been increasingly used to treat morning sickness and anxiety.

But doctors or other medical staff seldom advise about the risks faced by mothers-to-be.

The effect on neurons was similar to those previously identified in offspring exposed in the womb to cocaine or alcohol. 

‘As physicians caution pregnant women against alcohol and cocaine intake because of their detrimental effects to the fetus, based on our findings, it’s our recommendation they also advise them on the consequences of the use of cannabis during pregnancy,’ said Dr Melis. 

Large numbers of children are set to be exposed to its ingredients in the coming decades – before they are born.

This will happen if the potential risks of maternal use continue to be under-estimated and legalization policies move forward.

Rats are commonly used in research to model the effect of cannabis in humans. 

‘The present findings are critically important for unmasking and highlighting extensive neuro-biological maladaptations that increase the vulnerability of at-risk offspring to neuro-psychiatric disorders,’ said Dr Melis. 

Previous research has shown babies born to mothers who took cannabis while they were pregnant go on to experience problems with physical activity.

Chemicals called cannabinoids can be transferred from the mother to the offspring through the placental blood.

In the study published in Nature Neuroscience pregnant rats were given daily injections of a quantity of THC (tetrahydrocannabinol) equivalent to low doses in humans.

When the male offspring were confronted with an unstable bridge during pre-adolescence they were more likely to attempt the crossing than females – or unexposed peers. 

‘They were more prone to cross the bridge and displayed a markedly impaired evaluation of risk assessment,’ said Dr Melis. 

It’s a problem seen in many psychiatric diseases. Scans also showed dopamine in the VTA (ventral tegmental area) which is involved in reward and motivation, were hyperactive.

This is an area of the brain known to be involved in reward and motivation, explained Dr Melis.

She added: ‘Such persistently enhanced excitability of VTA dopamine neurons is a well-established neuro-developmental risk factor conferring vulnerability to psychiatric disorders.

‘This might manifest in difficulties in learning and reward processing, and provides an interpretative framework for clinical studies reporting maladaptive behaviours ranging from affective dysregulation to psychosis and addiction vulnerability in the offspring of mothers using cannabis during pregnancy.’

Her team was able to correct the behavioral and neural changes by treating the adolescent rats with pregnenolone.

This is a drug approved by the US Food and Drug Administration currently undergoing clinical trials for cannabis abuse, schizophrenia, autism and depression.

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