Threats of arrest, fines or quarantine do not encourage people to follow Covid-19 rules, while many admit they are not as diligent as they were in March.
The findings emerged in research carried out by NUI Galway and the Montreal Behavioural Medicine Centre (MBMC) in Canada to understand people's behaviour and motivations during the pandemic.
It comes as the Government rejected a recommendation to impose tough Level 5 restrictions nationwide here in favour of less strict Level 3 measures.
Dr Hannah Durand, iCARE collaborator and behavioural science researcher at NUI Galway, said: "After half a year of observing physical distancing, working remotely and wearing masks, one of the starkest warnings from the research is that we have evidence that a fatigue is setting in.
"Tellingly, people are consistently reporting the best motivator of adherence to physical distancing and other preventive measures is receiving feedback on how their behaviour is slowing the spread of the disease and saving lives. It suggests that behaviour may be changed by highlighting signs of success.
"We have also seen a surprising twist in how campaigns are received by the public. Threats of arrest, fines or quarantine do not appear to be helpful. Likewise, messages about the negative consequences of ignoring health recommendations - like an elderly relative will get sick and die - were found to be less effective than those that emphasised positive outcomes.
"This needs to be reflected in the ways we communicate with the public to bring about change in behaviour."
Just over 16pc of people who tested positive for Covid-19 or suspected they had the virus reported not self-isolating.
The top concern for people was that a relative who they do not live with would be infected with Covid-19 - eight in 10 were somewhat or greatly concerned about this.
It tends to be men more often than women, usually in their 20s and 30s, who are not following isolation measures in full. There are several explanations for this, including greater risk-taking propensity among young men. And young people are more likely to work in low-paid, public-facing jobs that make it difficult to adhere to restrictions.