Consumers have been warned most of them are on the wrong health plan.
The alert comes as two insurers are to impose price rises from next week, with warnings of more to come.
It is the second time this year that both Laya and Irish Life Health have increased prices. Vhi raised prices for its more than one million members in the summer.
Research by Dermot Goode of TotalHealthCare.ie has found three in five of those with health cover are on plans that are too costly or do not suit them.
This is particularly the case with older people.
He reviewed the buying behaviour of 1,000 policyholders since the start of the year. Mr Goode said it was important people do not auto-enrol on the same plan, especially if it is going up in price.
From Friday week both Laya and Irish Life will impose price rises for the second time this year.
Irish Life premiums rise by an average of 0.8pc from the start of November, in a move that will add between €30 and €70 a year to the cost for a family of two adults and two children renewing.
The company had raised the rate by 3.3pc from the start of June, or €30 annually, which means the cumulative increases will be between €60 and €100 for a family renewing from November.
Laya is to put up the price on 63 schemes by 1.7pc from November 1.
The company says this will result in an average annual increase of €25 per scheme. About half of the insurer's plans will increase.
Laya raised the price on 82 of its plans in July, with average increases of 2.9pc.
This means an extra €40 in payments a year per adult.
Cork-based Laya will also end its offer of free cover for children from Friday week.
In August Vhi said it was raising prices by an average of 6pc, blaming costs in hospitals, increases in consultants' fees and demand for more medical treatments by members.
The Vhi rises will see the cost of some of its premiums climbing by more than €300 a year.
Mr Goode said around three out of every five people who have cover are on the wrong plan or have an over-priced one.
This figure may be higher for those aged 60 or more.
Mr Goode said: "Older members continue to auto-renew cover most often due to a sense of loyalty and/or a fear of change.
"Dated plans are costing these members anything between €500 and €1,000 over and above what they really should be paying per adult."
He said there are likely to be more price hikes.