How do I find out if someone is infringing my patent?

A recurring founder worry sounds like this, “I can see their product on shelves. It looks like my invention. How do I know if it actually infringes my patent?” Indian headlines have shown how quickly such doubts turn into litigation, from Roche’s action against Cipla’s Erlocip for erlotinib hydrochloride to Merck’s suit over sitagliptin against Glenmark. In both, the patentee first pieced together market evidence, then mapped it to claim language, and only thereafter pressed the legal trigger. The Delhi High Court’s Division Bench eventually held Cipla liable for infringement of IN 196774, though it stopped short of a permanent injunction as the patent was nearing expiry and instead ordered accounts, a reminder that relief turns on precise claim comparison and timing.

Start with the fundamentals: is your patent enforceable today?

Before spending on investigations, confirm basic housekeeping.

• Term and renewals: Patents in India run for 20 years from the filing date, including PCT nationals from the international filing date. Non-payment of annuities causes lapse. You cannot enforce a lapsed or expired patent.
  

• Scope of exclusivity: Section 48 grants the right to prevent third parties from making, using, selling, offering for sale or importing the patented product, or using the patented process. That is the legal anchor for any infringement assessment.
  

• Defences and carve-outs: Expect the defendant to plead invalidity under Section 107 and, for pharma/biotech, the Section 107A “Bolar” safe harbour. Delhi High Court has read 107A broadly to cover exports for regulatory submissions abroad, subject to a reasonable relation test. Do not misread R&D or regulatory shipments as infringement without checking end-use.
  

Build the core: a claims-to-product/process mapping

Indian courts decide infringement by comparing each asserted claim to the rival product/process. The Delhi High Court Rules Governing Patent Suits, 2022 now require an infringement brief with precise claim charts, and correspondingly a non-infringement brief from the defendant. If you cannot map all essential elements, a suit will struggle.

Practical steps that usually work:

• Buy samples from the market, preserve chain of custody, photograph packaging and labels.
  

• For devices, teardown and lab testing. For chemicals, NABL-grade assays; for software-embedded products, protocol traces or standards conformance reports.
  

• Preserve online listings, brochures, and spec sheets, with dates.
  

For process patents, Section 104A can shift the burden: if the defendant’s product is identical to that made by your patented process, the court may direct the defendant to prove a different process. Delhi High Court has also signalled that 104A-style disclosures can be sought at an interim stage, so plead it early and precisely.

How courts actually test infringement: Indian jurisprudence you should know

Claim construction and “pith and marrow”

Indian courts adopt purposive construction. In Raj Parkash v. Mangat Ram (Delhi HC, 1978), the court looked at the “pith and marrow” of the invention and rejected non-literal, inessential tweaks as a defence to infringement. The message for founders is simple, cosmetic changes will not save a copier if your claim elements are present in substance.

Evidence-driven analysis in pharma disputes

In F. Hoffmann-La Roche v. Cipla (Delhi HC DB, 2015), after a full trial, Cipla’s Erlocip was held to infringe Roche’s claim to erlotinib hydrochloride. The court ordered accounts rather than an injunction because expiry was near. The ratio that matters for you, the court went by the claim language plus technical proof, not brand narratives.

Interim injunctions, public interest, and when courts will restrain

• In Merck v. Glenmark (Delhi HC DB, 20 March 2015), the Division Bench restrained the generic sitagliptin product after finding a strong prima facie case, irreparable harm, and balance of convenience with the patentee. Later orders refined interim directions, but the principle is clear, strong claim mapping plus credible validity wins early relief.
  

• In contrast, earlier in Roche v. Cipla (2008, single judge), interim relief was refused, citing public interest and a credible validity challenge. Interim outcomes are fact sensitive, and founders should be prepared for either pathway.
  

Cautionary note on validity and “no presumption”

The Bajaj Auto v. TVS litigation reminds us Indian courts are cautious with patents at interim stages and there is no sweeping presumption of validity. Strategy must therefore combine robust testing, clean claim charts, and readiness to meet invalidity grounds head-on.

Quick table: statute, cases, and what founders should do

What not to mistake for infringement

Two recurring FAQs arise at this stage:

Is experimental or regulatory use infringement?

Can Customs stop infringing imports of my patented product?

From suspicion to suit: a procedural mini-checklist

• Confirm status: Patent live, renewals paid, correct ownership recorded.
  

• Identify the act: Make, use, sell, offer to sell, or import under Section 48.
  

• Collect evidence: Purchase samples, preserve invoices, capture web listings; send to a credible lab or expert.
  

• Prepare claim charts: Align every essential element; include equivalents where appropriate. Use the Delhi HC Patent Suits Rules structure if suing in Delhi. 

• Screen defences upfront: Likely invalidity grounds under s.64 via s.107; consider whether 107A may apply to the other side’s acts.
  

• Process patents: Plead s.104A to seek disclosure or reversal of burden.
  

• Choose remedy: Interim injunction, accounts/damages, or inspection through a Local Commissioner for fact-finding at the outset, as per court practice.
  

Should you send a legal notice first?

Often yes, because it can open licensing dialogue and demonstrate good faith. But a poorly drafted threat can backfire. Section 106 allows the target to sue you for groundless threats. Keep communications factual, precise to claims, and free from overreach, or proceed straight to suit where appropriate. 

Where and how to sue

Under Section 104, sue in a court not inferior to a District Court. If the defendant counterclaims revocation, the matter transfers to the High Court. In Delhi, expect structured case management under the 2022 Patent Suits Rules, including claim construction, infringement, invalidity, and damages briefs. 

When will a court restrain quickly?

Founders often ask if “strong suspicion” is enough for an injunction. It is not. Courts look for: a prima facie case backed by solid claim charts and credible validity, irreparable harm, and balance of convenience. Merck v. Glenmark shows injunctions are possible where these converge. Roche v. Cipla at the interim stage shows public interest can cut the other way, but the final decision turned on careful claim analysis. Build your record accordingly.

Final takeaways for founders

• Treat claim charts as your north star. If you cannot draw them, you are not ready.
  

• For process inventions, move early under s.104A; do not wait till trial to seek disclosure.
  

• Anticipate 107/64 validity attacks and 107A safe harbour arguments; pre-butt them in your pleadings and evidence plan. 

• Be mindful of s.106 groundless threats if you send notices. 

• In Delhi, leverage the Patent Suits Rules, 2022 to structure your case filings and ask for targeted directions, including early technical primers and, where justified, inspection. 

If you suspect copying, your next move is not emotive, it is methodical: verify enforceability, gather testable evidence, chart claims meticulously, and then choose the right forum and remedy. The jurisprudence rewards precision.